Currently, USB (Universal Serial Bus) is a common interface technology which has a wide range of applications in daily life, e.g., USB flash drive, connecting a mouse or keyboard to a PC, USB removable disk. USB specifications include: USB 1.1, USB 2.0 and USB 3.0. USB 1.1 supports Low Speed (1.5 Mb/s) and Full Speed (12 Mb/s); USB 2.0 supports High Speed (480 Mb/s); and USB 3.0 supports Super Speed (5 Gb/s). Transmission cables for the USB interface are generally short and do not meet the requirements in certain application scenarios. For example, when a USB printer is not in the same place as the host (e.g., a computer) and is connected to the host via a USB transmission cable, the printer cannot work normally if the distance from the host is greater than 5 m. Moreover, in an application where the KVM (keyboard, video and mouse) and the host are not in the same place (for security or other reasons), the user can only operate the host through the KVM, which requires long-distance transmission of the USB signal. In security systems, long-distance transmission is also required for USB cameras.
Therefore, as technology develops, it is desirable to achieve long-distance transmission for the USB interface. Currently, signal transmission for a USB interface with a long transmission cable is achieved by: converting the USB signal into a networking-cable signal; transmitting the networking-cable signal by a networking cable; and converting the networking-cable signal into a USB signal. However, since transmission protocols in USB and networking cables are different, when the conventional method above is used, complex conversions from a USB signal to a networking-cable signal and from the networking-cable signal to a USB signal are required, which makes the signal transmission process cumbersome.